This will be interesting if it happens. The tracking system that looks for asteroids and near-Earth objects that could hit Earth, has found an asteroid that might hit Mars on 30th January 2008. Current data gives the odds of it hitting Mars as 1 in 75. Further measurements will narrow it down. Could provide a nice show and a peak under the surface of Mars due to the crater it would leave. Here’s hoping it does hit. And near one of the Mars rovers. More details at New Scientist.
Update: New data puts the chances of this impacting Mars as 1 in 25, or 4%. Though still small the odds are getting better.